Signal retransmission system



Patented Oct. 20, 1942 SIGNAL rRETRANSMISSION SYSTEM Manfred W. Muehter, Nutley, N. J., assignor to American District Telegraph Company,-Jersey City, N. J., a corporation of New Jersey Application muy 1.2.1939;ser'ia1 No. 283,938

2 Claims.

This invention relates generally to signaling systems adapted to' transmit signals from a subscribers station to a central office for the purlnaling systems whereiny it is desired to retransmit a subscribers signals to police or fire headquarters for the purpose of expediting effective lresponse to the various/types of alarms.

The conventional signaling system used for transmitting fire and burglary alarms to a central oilice comprises subscribers stations adapted to 'transmit signals by both grounding and interrupting the line circuit in either side thereof, the ksignals being received at the central ofce by' means of relays connected to either side of the line and battery or ground. This system is more generally known as the McCulloh circuit.

In accordance with this invention, the subscribers" signals are transmitted to the central oice` in the conventional manner but in order to 'economically utilize existing line facilities, it is found advantageous to retransmit the subscribers signalsfover the same subscribers circuit t'o one lor'more headquarters-stations. In accomplishing this result, it is necessary that al1 signals should be received in spite of grounds orbreaks in the transmission line and it is further necessary that retransmission be possible' without interference with' subscribers signals being'ltransmitted to the central oiii'ce.

Accordingly, the principal object of this inventionris to provide asystem for the retransmission' of either police of re alarm signals to one o'r more headquarters receivers over the conventional McCulloh circuit.

Another object of this `invention is to'provide a signaling system for retransmission to police orflre headquarters of a subscribers signals over the subscriber loop without interfering with the.V

reception of other subscribersV signals.

-It is a still'further object of this inventionto retransmit fire or police alarm signals to the proper headquarters stations without interfering with the receiving function of the relays within the McCulloh circuit.

Still another object of this invention is to provide, `in are or police alarm circuit, retransmission of `subscribers signals from the central oiilce to the headquarters stations in spite ci breaks or grounds in the transmissionline.

Further objects of this invention will be ap-k tion comprises a plurality of subscribers stations I connected in both sides of the transmission line 2 which extends between a number of headquarters stations indicated in the drawing as 3Il and 60 and a central office comprising the usual McCulloh receiving relays 3. Patent No. 253,080, issued to C'. F. McCulloh on January 31, 1882, shows a suitable' central oiiice circuit for use inthe applicants system. So far, the systern as described includes'the essential elements of the McCulloh signaling system described in detail in the above-mentioned patent with the exception of the headquarters receiving stations. In'order to retransmit signals received at the central office, it is necessary to provide a transmitter I0 which may be either manually or automatically'operated in accordance with the received signals. For'exarnple, the transmitter shown in Patent N o. 907,600 issued to R. M. Hopkins on December 22, 1908, is suitable for such purposes. Transmitter I0 interrupts the circuit from battery II to repeating relay I4 and thereby generates signals for retransmission. A recorder I6 is connected across battery II and Contact I5 of relay I4 for the purpose of locally providing'a record of the retransmitted signals.

To obtain retransmission of signals without interferenceV with subscribers signals', an alternating current source 24 is connected to contacts I8 and I9 of relay I4 through the transformer v22 and condensers 25 and 26 whereby relay I4 keys the alternating current to transmit signal'impu'lses to the transmission line 2 and hea'dquartersstations 30 and S0. The Vchoke coils 4 are connected between receiving relays 3 andtransmissionline 2 for preventing'actuation ofthese 'relays by the alternating current impulses transmitted' from contacts I8 and I9 while the condensers 25 and 26 prevent ow of direct current through the transformer 22 to ground.

The retransmitted signals are received at the headquarters stations and operate relays 33 and 34 which in turn operate the repeating relay 40 to control the recorder 45. The condensers 36 and 31 prevent the flow of direct current through the receiving relays 33 and 34 and at the same time pass the retransmitted alternating current signals. The choke coil 35 shunts vrelays 33 and 34 to allow the flow of Vdirect current through the transmission circuit 2 andat the same time prevents the alternating current impulses from being shunted Varound relays 33 andV 34. The relay includes a short-circuited winding 4I locatedv at the armature end which introduces a delay characteristic in theperformance of this relay to prevent actuation thereof by direct current charges-within the condensers 36- and 31 which build up as a result of the normal direct current potential of the closed subscribers loop faults or subscriber operation, the signals are retransmitted over the other side of the line. Or if a ground connection at the central ofce or the headquarters is faulty,the signals may still be transmitted throughv al series `circuit tc the Y headquarters receiving relays.

ing the attention of the headquarters operator to i l the recording of signals in recorder 45.

The headquarters stationv is similar inall respects to station 30 and therefore only lthe line connections are shown in the drawing for the purpose of indicating the manner of connecting a plurality of such stations. The choke coil is not connected at intermediate headquarters stations since it is unnecessary.

The operation of the system is started at the subscribers stations indicated by the numeral l on the drawing which alternately ground and break the transmission line 2 thereby alternately operating the central oiice relays 3 from battery 5. The relays 3 operating in accordancewith the system described in the above cited patent cause a` record to be made of the subscribers signal which may then be manually or automatically set up in transmitter I9. This transmitter breaks the circuit from battery H to relay I4 in the obvious manner to operate the contacts l5, I8 and I9. Contact l5 breaks the circuit from battery I l to the recorder I6 to provide a local record of retransmitted signals. The contacts |`8 and I3 impress alternating current voltage on both conductors of the transmission line 2 in accordance with the signalsV generated at transmitter lil.

Thus a circuit may be traced from one side of transformer 22 through condenser 25, contact I8 of reiay I4 over one side of transmission line 2 and through the subscribers stations, condenser 36 and relay 33 to ground. The contact I9 of relay i4 closes an obvious circuit over transmission line 2 to relay 34 at the headquarters station 30. Either of the relays 33 and 34 operating in series and closing their contacts, putsbattery on relay 4U which repeats the retransmitted impulses to recorder 45 through an obvious circuit.

If a subscribers station is operating in one side of the line to apply breaks and grounds to the transmission line, the retransmitted signals being applied to both sides of line 2 may still operate one of the relays 33 or 34 through the ground circuits. Thus the operation of a subscribers station or a plurality of them in one side of the line 2 does not prevent retransmission of signals to the headquarters stations. Choke coils 4 prevent interference between alternating and direct current signals at the McCulloh panel. If the ground at any of the headquarters stations becomes faulty, retransmission is carried on over both sides of transmission line 2 in series. This is possible because the E. M. F. in one half of the secondary winding of transformer 22 is opposite in phase tothat of the other half of the secondary.

From the above description of the system it is evident that subscribers may transmit their fire or police alarmV signals over eitherv side of the McCulloh circuit in the conventional manner, while the central cnice attendant may retransmit these signals to the police or iire headquarters over the subscribers loop circuit'without interfering with the subscribers circuit or the central office equipment. If the one side of the transmissionline is broken or grounded, either through Although only one modication of this invention has been described, it will be obvious to those skilled in the art that this invention is capable of several modications and therefore applicant desires that the invention shall be limited only by the prior art and the extent of the appended claims.`

I claim:

1. Iny a signalling system, a transmission line including a plurality of subscribers stations and a plurality of headquartersy stations therein, a central ofce connected to said transmission lline including a direct current sourcel and receiving relays connected to each side of said transmission line for receiving direct current signals from said subscribers stations, a transmitter at said 'central cnice for retransmitting the subscribers sig-V nals, a transmitting relay connected to said cen-- tral office transmitter ,and having contacts con-r nected to each side of Vsaid transmission line for keying it, an alternating current source connected between each ofsaid contacts and ground, choke coils connected to each of said receiving relays for blocking alternating currentY signals transmitted from said'central office transmitter and passing direct current signals from said sub" scribers stations, a pair of receivingl relays connected between each side of said transmission'line and ground at each of said headquarters stations, condensers connected in each side'of .said transmission line for blocking direct current signals from the subscribers stations, a repeating relay at each of said headquarters stations responsive to either or both of said receiving relays and having a .delayy characteristic rendering it non-responsive todirect current charges on said condensers and a signal receiver at each of saidv headquarters stations responsive to said repeating relay for indicating signals `received over either or both sides of Vsaid transmission line.

2. In a signalling system, a transmission line including a plurality of subscribers stations for transmitting direct current signal impulses,` a' central office connected to said transmissionv line including receiving'relays connected to each side thereof for receiving signalsffrom said subscribe ers stations, a plurality of headquarters stations connected in said transmission line, a transmitter at said central o'ice for retransmitting the subscribers signals to the headquarters stations by means of alternating current signals over veither or both sides of said transmission line, means at said central `office for blocking the alternating current signals from said receiving relays and Y passing direct current signals from said sub- -at each of saidheadquarters stations responsive to either or both of said receiving relays for indicating signals received over either or both sides of said' transmission line. 

